This invention relates to the field of display systems, more particularly to display systems using multiple light sources in combination with a spatial light modulator.
Many new types of displays systems have been developed that use a spatial light modulator or light valve in combination with an illumination source to project an image. These display systems are capable of providing high resolution, high contrast images having an excellent color gamut. One of the key criteria consumers use to distinguish various display systems is the brightness of the image. High image brightness is critical in the marketplace. High projector flux output enables high image brightness which enables viewers to clearly see the projected image, even in venues having a high ambient light level, and enables projection of very large images.
The brightness of the projected image is limited by the luminance, lumens per emitting area per solid angle, of the light source used in conjunction with the modulator. High output flux levels are especially difficult to achieve with small light valves such as the digital micromirror device (DMD(trademark)). The DMD, which is less than an inch across, has a small etendue or area-solid angle product.
Xenon and metal halide arc lamps are very high luminance light sources, but are unacceptable for many display system applications because of their short lifetimes, generally less than 2000 hours, high power requirements and safety concerns. A few arc lamps, such as high-pressure mercury lamps, have a long lifetime, between 6000 and 8000 hours, and a small etendue, but do not provide a high total flux. One technique that has been used to increase the brightness of a projected image is to use three lamps in combination with dichroic filters. The output of each lamp is filtered to provide a single primary colored light beam. The lamps sequentially are pulsed to peak the flux out of the lamp during a portion of the frame period. In concert, the three lamps act as a single sequential color source having a greater brightness than a single lamp. Unfortunately, pulsing the lamps reduces the stability of the arc and shortens the lifetime of the lamp.
What is needed is a long-life, high luminance, high flux light source that has a small etendue to enable efficient coupling to a small light valve.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention that provides a method and system for combining multiple light sources in light valve projectors. One embodiment of the claimed invention provides an integrating rod comprising: a first entrance face operable to transmit a first light beam, a first reflection face operable to reflect the first light beam, a second entrance face operable to transmit a second light beam, and an integrator body operable to transmit the first and second light beams to an exit face. Often a second reflecting face is included to reflect the second light beam. The integrating rod efficiently couples the two light beams into the integrator body where they are homogenized prior to exiting the integrator body.
The disclosed optical architectures enable two small-arc light sources to be used instead of one larger light source. The small-arc light sources have a much longer life and a smaller etendue that is more efficiently coupled to a small light valve such as a DMD.